OBJECTIVENuclear factor-kappa B (NF-kappaB) is a critical transcription factor governing the expression of many cytokines that are involved in the pathogenesis of inflammatory diseases, such as asthma and rheumatoid arthritis. Melatonin (MT), a relatively safe and potent antioxidant which has shown efficacy in several chronic inflammatory models, may inhibit the expression of NF-kappaB and therefore might have a therapeutic use in asthma. This study aimed at observing the effect of MT on the expression of NF-kappaB and airway inflammation in a rat model of bronchial asthma.

METHODSTwenty-four male Sprague-Dawley (SD) rats weighing 120 g to 170 g were randomly divided into three experimental groups (8 in each): (1) Asthmatic group: Rats were immunized on day 1 by intraperitoneal injection of 100 mg ovalbumin (OVA) in 1 ml of saline with 100 mg of alu minum hydroxide. From day 15 the animals were challenged with aerosolized OVA (1% in saline) for 20 minutes per day for 7 consecutive days. (2) MT group: OVA-sensitized rats were injected intraperitoneally with 10 mg/kg MT 30 minutes before each OVA challenge. (3) CONTROL GROUP: OVA for inhalation and MT for intraperitoneal injection was replaced with normal saline (NS). Airway responsiveness to aerosolized acetylcholine of 24 rats was detected six hours after the last challenge. Then the rats were lavaged and total and differentiated leukocytes counts in bronchoalveolar lavage fluid (BALF) were performed after staining with Wright-Giemsa staining. At the same time, levels of nitric oxide (NO) in BALF, inducible nitric oxide synthesis (iNOS) and constitute nitric oxide synthesis (cNOS) in the lung tissues were assessed with the use of nitrate reductase and chemical colorimetry, respectively. The expression of NF-kappaB in the lung tissues was observed by means of immunohistochemical staining.

RESULTS(1) After OVA challenge, there was a significant decrease in airway responsiveness, lymphocytes and eosinophils in BALF in MT group compared with asthmatic group (P < 0.01 respectively); (2) There was a significant decrease in amounts of NO(2)(-)/NO(3)(-) in the BALF and levels of iNOS in the lung tissues in MT group comparing with asthmatic group (P < 0.01 respectively); and the levels of iNOS in the lung tissues was correlated positively with NO(2)(-)/NO(3)(-) in the BALF (P < 0.01), but there were no significant differences in activity of cNOS in any of the groups analyzed. (3) There was a significant increase in expression of NF-kappaB in lung tissues in asthmatic group compared with the other groups (P < 0.01), and so was in MT group compared with control group (P < 0.05).

CONCLUSIONSMT could partially inhibit the expression of NF-kappaB and down-regulate the activity of iNOS in lung tissue, decrease the production of NO in BALF. These data suggest that the inhibitory effect of MT probably play a role in decreasing airway hyperresponsiveness and airway inflammation of asthmatic rats model.